Abstract：
Somatostatin, a peptide hormone that activates G-protein-coupled receptors, inhibits the secretion of many hormones. This study investigated the mechanisms of this inhibition using amperometry recording of Ca2+-triggered catecholamine secretion from mouse chromaffin cells. Two distinct stimulation protocols, high-KCl depolarization and caffeine, were used to trigger exocytosis, and confocal fluorescence imaging was used to monitor the rise in intracellular free Ca2+. Analysis of single-vesicle fusion events (spikes) resolved the action of somatostatin on fusion pores at different stages. Somatostatin reduced spike frequency, and this reduction was accompanied by prolongation of pre-spike feet and slowing of spike rise times. This indicates that somatostatin stabilizes initial fusion pores and slows their expansion. This action on the initial fusion pore impacted the release mode to favour kiss-and-run over full-fusion. During a spike the permeability of a fusion pore peaks, declines and then settles into a plateau. Somatostatin had no effect on the plateau, suggesting no influence on late-stage fusion pores. These actions of somatostatin were indistinguishable between exocytosis triggered by high-KCl and caffeine, and fluorescence imaging showed that somatostatin had no effect on stimulus-induced rises in cytosolic Ca2+. Our findings thus demonstrate that the signalling cascades activated by somatostatin target the exocytotic machinery that controls the initial and expanding stages of fusion pores, while having no effect on late-stage fusion pores. As a result of its stronger inhibition of full-fusion compared to kiss-and-run, somatostatin will preferentially inhibit the secretion of large peptides over the secretion of small catecholamines. KEY POINTS: Somatostatin inhibits the secretion of various hormones by activating G-protein-coupled receptors. In this study, we used amperometry to investigate the mechanism by which somatostatin inhibits catecholamine release from mouse chromaffin cells. Somatostatin increased pre-spike foot lifetime and slowed fusion pore expansion. Somatostatin inhibited full-fusion more strongly than kiss-and-run. Our results suggest that the initial fusion pore is the target of somatostatin-mediated regulation of hormone release. The stronger inhibition of full-fusion by somatostatin will result in preferential inhibition of peptide release.
摘要：
生长抑素,一种激活G蛋白偶联受体的肽激素，抑制许多激素的分泌。这项研究使用安培法记录小鼠嗜铬细胞中Ca2触发的儿茶酚胺分泌，研究了这种抑制的机制。两种不同的刺激方案,高KCl去极化和咖啡因，被用来引发胞吐，共聚焦荧光成像用于监测细胞内游离Ca2+的升高。对单囊泡融合事件（尖峰）的分析解决了生长抑素在不同阶段对融合孔的作用。生长抑素降低了尖峰频率，这种减少伴随着刺前脚的延长和刺突上升时间的减慢。这表明生长抑素稳定初始融合孔并减缓其扩张。对初始融合孔的这种作用影响了释放模式，有利于亲吻并运行，而不是完全融合。在峰值期间，融合孔的渗透率达到峰值，下降，然后进入高原。生长抑素对高原没有影响，表明对后期融合孔没有影响。生长抑素的这些作用在高KCl和咖啡因引发的胞吐作用之间无法区分，和荧光成像显示生长抑素对刺激诱导的胞浆Ca2+升高没有影响。因此，我们的发现表明，生长抑素激活的信号级联靶向控制融合孔的初始和扩张阶段的胞吐机制，而对后期融合孔没有影响。由于与亲吻和奔跑相比，其对完全融合的抑制作用更强，生长抑素将优先抑制大肽的分泌而不是小儿茶酚胺的分泌。关键点：生长抑素通过激活G蛋白偶联受体抑制各种激素的分泌。在这项研究中,我们使用安培法研究生长抑素抑制小鼠嗜铬细胞释放儿茶酚胺的机制。生长抑素可增加钉足前寿命并减慢融合孔扩张。生长抑素比亲吻和奔跑更强烈地抑制完全融合。我们的结果表明，初始融合孔是生长抑素介导的激素释放调节的目标。生长抑素对完全融合的更强抑制将导致肽释放的优先抑制。
